This invention relates to the positioning of the output shaft of a motor and, more paticularly, the positioning of the output shaft wherein the motor is under control of a counter which responds to both a predetermined count and to pulses generated by the output shaft of the motor as it is rotated.
Although the present application can be used for controlling many types of devices, it is particularly suitable for adjusting the control point in condition controlling systems from a remote point. In building automation systems, remote points are connected over a transmission channel to a central processing unit. The remote points may be temperature sensing thermostats, fans, chillers, dampers, and other devices relating to the control of the environment within a building. The central processing unit, either under control of an operator or under program control, uses the sensor inputs to control the temperature and humidity of the various zones throughout the building. When the central processing unit wishes to change the temperature at a remote zone, for example, for night setback or morning pickup, it transmits a signal representing the desired new condition which then adjusts the control point of the condition controlling system at the remote location. The condition controlling system then compares the new control point with the present condition as measured by the condition sensing sensor for taking the proper action to bring the actual condition to the desired condition.
Present control point adjustment mechanisms are plagued by a multitude of problems. The bi-directional motors which are used in present systems are troubled with high hysteresis; that is, if the motor is to be driven to a specific control point, there will be a discrepancy between the desired point and the actual point depending upon the direction in which the motor is driven. Also, the number of points at which the motor can be stopped in its full circle of rotation is not as great as it could be and, therefore, the present systems suffer from low resolution. Moreover, present systems suffer from no memory in the case of power failure; that is, if power fails the control point adjustment device will wander away from the point of the last setting.